1. Field of the Invention
The present invention relates generally to brittle nonmetallic workpieces and methods and devices for making the same, more particularly to a brittle nonmetallic workpiece with a curved edge and a method and a laser cutting device for making the same.
2. Discussion of the Related Art
Typical methods for cutting glass or other brittle nonmetallic substrates are based on the use of a diamond or a small rotary cutter to first produce a scribed line in the glass, in order to then split the glass by application of an external mechanical force along the scribed line. A disadvantage of this method is that the scribed line causes fragments to be released from the surface. The fragments stay on the glass and make scratch to it. Furthermore, the micro-cracks produced in the cut edge during the scribing process lead to reduce mechanical stressability, that is, to increase risk of breakage. An approach for preventing the formation of fragments as well as chips and micro-cracks is to cut glass based on thermally induced mechanical tension. In this approach, a laser beam emitting from a laser cutting device, directed at the glass is moved at a predetermined speed relative to the glass, thereby producing a crack in the glass. Then, the glass is split mechanically.
Referring to FIG. 8, a typical laser cutting method for cutting a brittle nonmetallic substrate 10 includes following steps. An original crack 101 is formed on a surface of a brittle nonmetallic substrate 10 with a diamond cutter. The original crack 101 overlaps a starting point of a predetermined cutting straight line L1. A laser beam is focused on the brittle nonmetallic substrate 10 to form an elliptic beam spot 111. The elliptic beam spot 111 moves along the predetermined cutting straight line L1 from the original crack 101, and keeps a major axis b of the elliptic beam spot 111 aligned with the predetermined cutting straight line L1. Therefore, a thermal energy of the elliptic beam spot 111 is symmetrically distributed at two sides along the predetermined cutting straight line L1. Simultaneously, a sprayer follows the elliptic beam spot 111, and ejects a coolant stream 12 on the brittle nonmetallic substrate 10 along the predetermined cutting straight line L1. As a result, a crack is formed in the brittle nonmetallic substrate 10 along the predetermined cutting straight line L1. However, if a predetermined cutting line is curved, the major axis b of the elliptic beam spot 111 cannot be substantially aligned along a tangent of a specific point on the predetermined cutting line when the brittle nonmetallic substrate moves relative to the laser beam according to the predetermined cutting line. Therefore, the thermal energy of the elliptic beam spot 111 is not symmetrically distributed on the brittle nonmetallic substrate along the predetermined cutting line. Thus, a crack may not be formed according to the predetermined cutting line.
Referring to FIGS. 9 and 10, in order to cut a brittle nonmetallic substrate 20 along a predetermined curved cutting path, another typical laser cutting method is provided. A laser beam 21 scans, such as to form a linear beam spot 211 on the brittle nonmetallic substrate 20. A laser cutting device 24 includes a first reflective mirror 241, a second reflective mirror 242, and a controller 243. The first reflective mirror 241 can oscillate about a vertical scanner axis K1, and the second reflective mirror 242 can oscillate about a horizontal scanner axis K2. The vertical scanner axis K1 is perpendicular to the horizontal scanner axis K2. The controller 243 is configured for controlling oscillations of the first reflective mirror 241 and the second reflective mirror 242. The laser beam 21 moves relative to the brittle nonmetallic substrate 20 along the X-axis via the oscillation of the first reflective mirror 241. The laser beam 21 moves relative to the brittle nonmetallic substrate 20 along the Y-axis via the oscillation of the second reflective mirror 24. Therefore, a linear beam spot 211 can be formed to irradiate on the brittle nonmetallic substrate 20 by the laser cutting device 24.
A contour of the linear beam spot 211 is changed by the laser cutting device 24 according to the predetermined curved cutting path L2, thus making the linear beam spot 211 overlap a part of the predetermined curved cutting path L2 all the time. Simultaneously, a coolant stream 22 moves following the linear beam spot 211, and along the predetermined curved cutting path L2. As a result, a crack is formed in the brittle nonmetallic substrate 20 along the predetermined curved cutting path L2. Finally, the brittle nonmetallic substrate 20 is split along the crack by application of an external mechanical force on the brittle nonmetallic substrate 20.
However, the contour of the linear beam spot 211 need to be continuously changed by the laser cutting device 24 in a cutting process. That is, positions of the first reflective mirror 241 and the second reflective mirror 242 need to be continuously changed. The process of controlling the two reflective mirrors is difficult. In addition, the first reflective mirror 241 and the second reflective mirror 242 not only oscillate about scanner axes K1, K2 respectively, but also move according to the predetermined curved cutting path L2. Thus, the cutting process is error-prong.
Therefore, a brittle nonmetallic workpiece and a method and a laser cutting device for making the same to solve the aforementioned problems is desired.